Field of the Invention
The present invention relates to a method for operating an ignition device, in particular a magneto ignition system or device, for an internal combustion engine. It also concerns an ignition device operating in accordance with said method.
Description of the Background Art
Ignition devices of this nature are typically used in hand-operated tools powered by an internal combustion engine. To determine speed, an electronics unit analyzes at least one voltage signal with positive and negative half-waves produced by generator action, which is to say induced by means of an electromagnet (magnet generator). With the customary construction of such an ignition device having a magnetic pole wheel coupled to the internal combustion engine, for example to its crankshaft, and having a typically U-shaped iron core with a coil (trigger, charging, and/or ignition coil) located on at least one of the core legs thereof, the rotation of the magnetic pole wheel equipped with permanent magnets results in an induced voltage in the relevant coil, wherein the coil voltage has negative and positive half-waves. The electronics unit infers the speed and, in particular, also the direction of rotation of the magnetic pole wheel from the time-dependent and/or rotation-angle-dependent sequence of positive and negative half-waves. Active components, in particular transistors, and a microprocessor are used to determine the speed and/or angular positions, as well for any signal processing.
It is known from DE 102 01 422 A1 that an air gap between the magnetic pole wheel and the core leg that varies or is subject to dispersion can affect the voltage amplitude of the coil signal, in particular of the trigger coil, in exactly the same way as varying strength of the pole wheel magnet, which in turn can cause an incorrect determination of angular position. In order to ascertain a correction factor, it is proposed there to compare the angular position determined through a positive or negative threshold exceedance with a mean angular position that can be ascertained from the typical AC voltage pattern of the coil signal or trigger signal. Since there is no load dependence at the time of a threshold analysis, it is assumed there that the two angular positions ascertained from the mean value and from the threshold analysis would normally have to be equal. A change in an air gap and/or magnet strength can then be inferred from a deviation.